Theresa May's deal on Brexit is heading for defeat in Parliament. That could lead to no deal, the negotiation of a different deal, a general election, a second referendum – or MPs swallowing the package at the second attempt.

EU-Turkey relations have deteriorated sharply in recent years, and even maintaining transactional co-operation could become increasingly difficult. The challenge for Europe is how to prevent relations from souring further.

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Theresa May's deal on Brexit is heading for defeat in Parliament. That could lead to no deal, the negotiation of a different deal, a general election, a second referendum – or MPs swallowing the package at the second attempt.

Researchers at the Centre for European Reform, a London think tank focused on European Union policy, estimate the economy was 2.5% smaller at the end of the second quarter than it would have been had voters chosen in 2016 to stay in the EU.

Alternatively, she doesn’t get her deal through (for an explanation of the different scenarios of what happens then, see the summary by Charles Grant of the Centre for European Reform). That will essentially depend on whether MPs who would rather hold on to the deal for fear of something worse are outnumbered by those who hope that by refusing it they can get something better.

“Last summer, the chances of this outcome seemed minimal,” wrote Charles Grant, director of the Centre for European Reform, a London-based research institute, in a briefing paper. But the odds have improved, he said, because the opposition Labour Party is now more positive about that notion if it cannot achieve its favored outcome, which is a general election.

The closest the EUBG has come to being used was five years ago, when "the UK blocked it from supporting French operations in the Central African Republic, fearful of the potential effect on Britain's EU membership debate", according to the Centre for European Reform.

If parliament rejects the Brexit deal agreed between the UK and the EU, think-tank the Centre for European Reform has some ideas about what could come next. A CER report outlines five possible options: no deal, renegotiation of a different deal, a general election, a second Brexit referendum, or MPs finally accepting the deal.

When you look at all the options (summarised here by Charles Grant of the Centre for European Reform… there’s also some gaming of the scenarios here by Stefanie Bolzen and Philip Crowley) you could see how options once thought impossible could look plausible given the blocked-off paths everywhere else.

As John Springford at the Centre for European Reform has written, the choice is very clear: remain in an all-UK customs union, or leave and accept the need for a customs border in the Irish Sea that leaves Northern Ireland in a different relationship to the EU.

The Irish-only backstop has not so much disappeared as been folded into the all-UK one. As trade expert Sam Lowe said in a tweet: “[Northern Ireland]-specific ultimate insurance policy will live; will just be a question of how many law degrees you need to find it.”

Sam Lowe, a senior research fellow at the Centre for European Reform think tank, said the constraints of an UK-EU customs union were substantial. “Whilst in a customs union with the EU, the UK will be required to fully align its external tariff with that of the EU’s, meaning it cannot lower or remove tariffs either unilaterally or as part of a new free trade agreement.”

So what could the political declaration look like? Well, according to the Centre for European Reform think-tank, chief negotiator Michel Barnier says that it could include “points of convergence” such as foreign policy, military cooperation, and UK participation in research programmes after 2020. But there will be no clarity on the future UK/EU economic partnership.